Geographical planning of space quarterly journal

Geographical planning of space quarterly journal

Modification of the Turc Model Coefficient for Estimating Reference Evapotranspiration in Windy Regions of Iran

Document Type : Articles extracted from Thesis

Authors
1 Department of Water Engineering, Faculty of water and soil, University of Zabol, Zabol, Iran
2 Department of Water Engineering, Faculty of Water and Soil, University of Zabol, Zabol, Iran
10.30488/gps.2026.542318.3859
Abstract
Combination-based equations such as the Penman-Monteith (PM) model provide robust estimates, they require extensive meteorological data, which are often unavailable. Simpler empirical models such as the Turc (T) model which relies primarily on radiation and temperature are widely adopted as practical alternatives. In addition to radiation and air temperature, wind speed plays a critical role, particularly in regions prone to high winds. This study investigates the impact of wind speed on the accuracy of the Turc method and to develop a modification coefficient for the mentioned model in seven windy regions of Iran, including Ardabil, Aligoodarz, Bijar, Torbat-e Jam, Rafsanjan, Zabol, and Manjil. The study utilized 25 years of daily meteorological observations. The original coefficients of the Turc model group were not suitable for the stations in Aligoodarz, Bijar, Torbat-e Jam, Rafsanjan, Zabol, and Manjil. The best corrective coefficients for the selected model at the Aligoodarz and Bijar stations, calculated using the sum of squared errors method, were 0.18 and 0.0169, respectively. For the stations in Torbat-e Jam, Rafsanjan, Zabol, and Manjil, a regression relationship was established between wind speed and the corrective coefficient of the selected model. The ET0 values obtained through this approach exhibited excellent agreement with the standard Penman-Monteith (PM) method, as evidenced by NRMSE values of 0.04, 0.05, 0.07, and 0.06, respectively, and EF values exceeding 0.98 for all four stations. In contrast, for the Ardabil station, the original coefficients of the Turc model group yielded acceptable results, with an NRMSE below 0.21.
Keywords
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